This invention relates to a brush-commutated direct-current motor.
Such brush-commutated direct-current motor comprises a stator with a plurality of exciter poles and a rotor rotatable relative to the stator about an axis of rotation. The rotor has a plurality of pole teeth and grooves arranged between the pole teeth, which separate the pole teeth from each other along a circumferential direction around the axis of rotation. On the pole teeth coil windings are arranged, which in operation of the brush-commutated direct-current motor are energized via a commutator arranged on the rotor and in this way produce an electromotive force on the rotor by interacting with the exciter poles of the stator. The commutator comprises a plurality of lamellae to which the coil windings of the rotor are connected via connecting arms.
In the manufacture of brush-commutated direct-current motors it can be provided to mount a plurality of coil windings on each pole tooth, in order to thereby reduce the wire thickness required for the manufacture of the coil windings. When merely one coil winding would be arranged on each pole tooth, the same would require a wire of comparatively large wire thickness, which renders processing of the wire for winding around the pole teeth comparatively difficult. By mounting a plurality of coil windings on each pole tooth, the wire thickness of the wire used can be reduced, so that the manufacturing process in general turns out to be easier.
As described in FR 2 841 399 A, a first winding cycle and a second winding cycle, in each of which a coil winding is arranged on each pole tooth, conventionally are carried out in an identical way.
Because the coil windings on the pole teeth are wound in different winding cycles, coil windings which differ in their position however are obtained on each pole tooth. A succeeding coil winding of a later winding cycle now is wound onto a coil winding from a preceding winding cycle, which leads to the fact that the wire length of the outer coil winding wound at a later time is larger and thus in operation parallel branches of coil windings are obtained, which can differ in their electrical resistance—due to the different wire length. This can lead to asymmetries in the commutation current.
In addition, hybrid winding arrangements nowadays are known, in which the coil windings arranged on a pole tooth are not connected with the same lamellae, but are connected to different lamellae. For example, from U.S. Pat. No. 7,821,170 B2 and EP 1 489 724 B1 brush-commutated direct-current motors are known, in which on each pole tooth a first coil winding is mounted in a first winding direction and a second coil winding is mounted in an opposite, second winding direction. Because in such winding arrangements the connecting arms with which the different coil windings of a pole tooth are connected to the respectively associated lamellae possibly intersect, laying of the connecting arms towards the associated lamellae possibly may not be easy to do—in particular with a view to the available installation space.